Aerial feeder arrangement



Sept. 20, 1938. c. s. FRANKLIN 2,130,387

' AERIAL FEEDER ARRANGEMENT Filed July 25, 1936 INVENTOR CHARLES SAMUEL FRANKLIN ATTORNEY UNITED STATES PATENT OFFICE AERIAL FEEDER ARRANGEIWENT Charles Samuel Franklin, London, England, assignor to Radio Corporation of America, a corporation of Delaware Application July 25, 1936, Serial No. 92,548 In Great Britain August 31, 1935 'eelaims. (01. 250-33) This invention relates to aerial feeder arrangements.

In one of the most commonly employed aerial feeder arrangements wherein the high frequency energy to be radiated is transmitted to the aerial by means of a concentric tube feeder, it is usual to provide a good earth at the feeder termination in addition to suitable impedance matching means. If the earth connection is not good, i. e., if the resistance and impedance between the outer tubular conductor of the feeder and earth is not sufficiently low, a certain loss of energy occurs with consequent apparent reduction in the efficiency of the aerial and this gives rise to difficulties in situations where a satisfactory earth connection is not available.

Similar losses occur in the case of receiving arrangements wherein the aerial is connected through a feeder to the receiver proper, and the present invention, which is applicable equally to transmitting or receiving aerials or feeders, has for its object to provide an improved aerialfeeder arrangement wherein the difiiculty above referred to is avoided and earthing of the tubular feeder at the termination thereof is rendered unnecessary.

According to this invention a radio transmitting or receiving installation comprises at least one pair of similar aerials, a pair of lines associated one with each of said aerials, one of said lines being a half wavelength or an odd plurality of half wavelengths longer than the other, and a high frequency cable associated with said lines through a transformer device, the whole arrangement being such that when the currents in the aerials are equal and in phase those in the lines are equal and in opposite phase, and there is no earth current at the transformer device end of the high frequency cable. With such an installation an earth connection can be dispensed with entirely.

The invention is illustrated in the accompanying drawing which shows diagrammatically one embodiment thereof.

Referring to the drawing, AB, CD represent two vertical aerials extended parallel to one another and only a small fraction of a wavelength apart, each being a plurality of half wavelengths long and of the type in which radiation from alternate half wavelengths is suppressed or partially suppressed, as shown by incorporating half wavelengths X folded back upon themselves. If the currents in these aerials are substantially equal and in phase, the radiation from the pair will be substantially equal in all directions round them; in other words the pair of aerials constitute a unidirectional aerial system. The aerials are fed at their bases through two lines BF, DEG, the latter being one-half wavelength longer than the former. As shown, the extra half wavelength in DEG is constituted by the half wavelength DE at the top end thereof and which is folded back upon itself so as to be substantially non-radiating. Thus, if the phases of the currents in BF and EG are opposite, those of the currents in the aerials will be the same and, although the radiation from the aerials will be additive that from the lines BF, DEG will be mutually cancelling. At their bottom ends the lines BE, DEG are connected, at F and G to a half wave feeder section J; G being also the point of connection to a main feeder H leading to a transmitter or receiver (as the case may be) not shown. The section J could be an odd plurality of half wavelengths long. The feeder H and the half wave feeder section J are of the air-spaced, concentric, tubular, high frequency cable type, and K represents insulators through which the lines BF, DEG are passed. The half wave feeder section J constitutes a transformer ensuring opposed phase energization at the points F and G.

The feeder H should be of correct surge impedance to match the impedance of the aerial and line system as measured at the point G. Alternatively, suitable impedance transforming means, as known per se, may be interposed between the point G and the main feeder H.

It will be observed that the currents in BE and EG are equal and in opposite phase and also the currents in the inner and outer conductors of the feeder H are also equal and in opposite phase. Accordingly, if the main feeder H be earthed at the end where the half wave section J is located, there will be no earth currents. In other words, earthing is unnecessary and the system therefore offers particular advantages for installation on to the tops of buildings or in desert surroundings where the obtaining of a good earth is a matter of difficulty.

Obviously the invention is not limited to the use of the particular type of aerial illustrated. For example, cage aerials could replace the aerials AB, CD or a number of pairs of aerials as illustrated could be employed in combination to provide desired directional effects.

What is claimed is:

1. A radio transmitting or receiving installation comprising at least one pair of similar aerials the signal currents in said aerials being equal and in phase, a pair of lines associated one with each of said aerials, one of said lines being an odd multiple of a half wavelength, including unity, longer than the other whereby the signal currents at the end of said line opposite the aerials are equal and in opposite phase, a high frequency cable associated with said lines and a transformer device between said lines and said cable for reversing the phase of current supplied to a conductor of said cable whereby there is no earth current at the transformer device end of the high frequency cable.

2. An installation as claimed in claim 1 wherein the longer line is connected to its aerial through an interposed, substantially non-radiating half wavelength of conductor.

3. A radio transmitting or receiving installation comprising a main high frequency cable of the concentric tubular air-spaced type, a half wave section of high frequency cable of the concentric tubular air-spaced type having its outer conductor connected to the outer conductor of the main cable and its innerconductor connected at one endtd the adjacent end of the inner conductor of the main cable, a pair of closely spaced vertical line s one of said lines being connected at the bottom to said end of the inner conductor of the main cableand the other of said lines being connected at the bottom to theother end of the inner conductor'of the said cable section, said one line having at its upper end a substantially nonradiating half wavelength of conductor and a pair of closely spaced vertical aerials, one of said aerials being connected at the bottom through said half wavelength of conductor to the top of said one lineand the other of said aerials connected atthebottom tothe top of said other line.

4. A radio'transmitting or receiving installaconductor of the main cable and the other of said ,10

' lines being connected at the bottom to the other end of the inner conductor of the said cable section, said one line having at its upper end a substantially non-radiating half wavelength of conductor and a pair of vertical aerials, one of said aerials being connected at the bottom through said half wavelength of conductor to the top of said one line and the other of said aerials connected at the bottom to the top of said other line. i T

installation as definedin claim 4, characterized in this that said aerials are similar, each a plurality of half wavelengths long, of the type in which radiation from alternate half wavelengthsis substantially suppressed.

6. A radio transmitting or receiving installation comprising at least one pair of similar aerials, a pair of lines associated one with each of said aerials, one of said lines being an odd multiple of a half wavelength, including unity, longer than the other, and means for exciting correspondingly located points on said lines with currents of opposite instantaneous polarities, the whole arrangement being such that when the currents in the aerials are equal and in phase, those in the lines are equal and in opposite phase.

CHARLES SAMUEL FRANKLIN. 

